Hook; Microprocessor Clock Synthesizer; Serial Peripheral Interface (Spi) - Motorola GM950E Service Manual

Controller
When the IGNITION input goes below 6 volts, Q0421 switches off and R0426, R0427 pull line
IGNITION SENSE high. The software is alerted by line IGNITION SENSE to switch off the radio by
setting B+ CONTROL to low. The next time the IGNITION input goes above 6 volts the above
process will be repeated.
2.6

Hook

The HOOK input is used to inform the µP when the Microphone´s hang-up switch is engaged.
The signal is routed from J0101-3 and transistor Q0137 to the E9/20µP U0101-56. The voltage
range of HOOK in normal operating mode is 0-5V. If a rear GP input line is set as HOOK then the
front HOOK signal is overriden.
2.7

Microprocessor Clock Synthesizer

The controller uses the oscillator in the microprocessor E9/20µP along with some external
components (C0115-C0117, L0114, R0115, Y0114) to generate the clock. Q0114 is used to alter
the clock frequency slightly under software control if there is a possibility of harmonics of this clock
source interfering with the desired radio receive frequency.
2.8

Serial Peripheral Interface (SPI)

The µP communicates to many of the IC's through its SPI port. This port consists of SPI TRANSMIT
DATA (MOSI) (E9/20µP:U0101-52), SPI RECEIVE DATA (MISO) (E9/20µP:U0101-51), SPI CLK
(E9/20µP:U0101-53) and chip select lines going to the various IC's, connected on the SPI PORT
(BUS). This BUS is a synchronous bus, in that the timing clock signal CLK is sent while SPI data
(SPI TRANSMIT DATA or SPI RECEIVE DATA) is sent. Therefore, whenever there is activity on
either SPI TRANSMIT DATA or SPI RECEIVE DATA there should be a uniform signal on CLK. The
SPI TRANSMIT DATA is used to send serial from a µP to a device, and SPI RECEIVE DATA is used
to send data from a device to a µP. The only device from which data can be received via SPI
RECEIVE DATA is the EEPROM (U0108)
On the controller there are three ICs on the SPI BUS, AFIC (U103-33), EEPROM (U0108-1) and
D/A (U0731-6). In the RF sections there is one IC on the SPI BUS, the FRAC-N Synthesizer. The
SPI TRANSMIT DATA and CLK lines going to the RF section are filtered by L0194/L0195 to
minimize noise. The chip select lines for the IC´s are decoded by the address decoder U102.
The SPI BUS is also used for the control head. U0104-1,2 buffer the SPI TRANSMIT DATA and CLK
lines to the control head. U0104-3 switches off the CLK signal for the LCD display if it is not selected
via LCD CE.
When the µP needs to program any of these IC's it brings the chip select line for that IC to a logic 0
and then sends the proper data and clock signals. The amount of data sent to the various IC's are
different, for example the FRAC-N can receive up to 13 bytes (97 bits) while the DAC can receive up
to 3 bytes (24 bits). After the data has been sent the chip select line is returned to a logic 1.
The Option board interfaces are different in that the µP can also read data back from devices
connected.
6.3-4 Theory of Operation